Issue serving Swagger file in a containerised go app - go

Question

I'm currently writing an app in go. I've never done this in go before so please be patient. I'm trying to happily serve my swagger doc via docker.
I'm using redoc/redocly but when I containerise my app, I can no longer access the endpoint I've configured to serve the swagger doc.
Here is the code regarding swagger I have within my app:
sm := mux.NewRouter()
opts := middleware.RedocOpts{SpecURL: "/swagger.yaml"}
sh := middleware.Redoc(opts, nil)
sm.Handle("/docs", sh)
sm.Handle("/swagger.yaml", http.FileServer(http.Dir("./")))
s := &http.Server{
Addr: ":8080", // configure the bind address
Handler: sm, // set the default handler
ReadTimeout: 1 * time.Second, // max read time out for client
WriteTimeout: 1 * time.Second, // max time to write response to client
IdleTimeout: 120 * time.Second, // max time for connections using TCP keep-alive
}
go func() {
err := s.ListenAndServe()
if err != nil {
os.Exit(1)
}
}()
Apparently I can serve static files using in-built fileserver in go-lang that I've tried to do.
The above works as intended when I run the app from within VS Code.
However when I containerize the code and run the docker container, I don't see the swagger doc served in the nice UI when I navigate to http://localhost:8080/docs.
When I check network tools in my web browser e.g Chrome it shows the following error:
Error: Failed to load http://localhost:8080/swagger.yaml: 404 Not Found
Can someone please tell me what I'm doing wrong?
Do I need to do make modifications to the code or the Dockerfile so I can get redocly to serve the file.
UPDATE
I'm sharing my Dockerfile
FROM golang:1.16-alpine AS builder
# Set necessary environmet variables needed for our image
ENV GO111MODULE=on \
CGO_ENABLED=0 \
GOOS=linux \
GOARCH=amd64
# Move to working directory /build
WORKDIR /build
COPY go.mod .
COPY go.sum .
RUN go mod download
COPY . .
# Build the application
RUN go build -o main .
WORKDIR /dist
# Copy binary from build to main folder
RUN cp /build/main .
# Build a small image
FROM scratch
COPY --from=builder /dist/main /
EXPOSE 8080
# Command to run when starting the container
ENTRYPOINT ["/main"]